KCa channels and epoxyeicosatrienoic acids: major contributors to thermal hyperaemia in human skin

Evidence of premature vascular dysfunction in young adults who regularly use e-cigarettes and the impact of usage length

BACKGROUND

Electronic (e-) cigarettes are increasingly popular tobacco products on the US market. Traditional tobacco products are known to cause vascular dysfunction, one of the earliest indicators of cardiovascular disease (CVD) development. However, little is known about the effect of regular e-cigarette use on vascular function. The purpose of this study was to investigate the impact of regular e-cigarette use on vascular function and cardiovascular health in young, healthy adults.

METHODS

Twenty-one regular users of e-cigarettes (ECU) and twenty-one demographically matched non-users (NU) completed this study. Vascular health was assessed in the cutaneous microcirculation through different reactivity tests to evaluate overall functionality, endothelium-dependent vasodilation (EDD), and endothelium-independent vasodilation (EID). Macrovascular function was assessed using flow-mediated dilation (FMD).

RESULTS

Our results suggest that regular users of e-cigarettes present with premature microvascular impairment when compared to non-users. Specifically, they exhibit lower hyperemic (p = 0.003), thermal (p = 0.010), and EDD (p = 0.004) responses. No differences in EID between the groups were identified. We also identified that individuals who use e-cigarettes for longer than 3 years also present with systemic manifestations, as observed by significantly reduced macrovascular (p = 0.002) and microvascular (p ≤ 0.044) function.

CONCLUSIONS

Our novel data suggests that young, apparently healthy, regular users of e-cigarettes present with premature vascular dysfunction in the microcirculation when compared to non-users. We have also identified systemic vascular dysfunction affecting both the micro and macrovasculature in those young individuals who used e-cigarettes for longer than 3 years. Taken together, these findings associate regular e-cigarette use with premature vascular dysfunctions and adverse cardiovascular outcomes.

Inhibition of superoxide and iNOS augment cutaneous nitric oxide-dependent vasodilation in non-Hispanic black young adults

We assessed the combined effect of superoxide and iNOS inhibition on microvascular function in non-Hispanic Black and non-Hispanic White participants (n = 15 per group). Participants were instrumented with four microdialysis fibers: (1) lactated Ringer's (control), (2) 10 μM tempol (superoxide inhibition), (3) 0.1 mM 1400 W (iNOS inhibition), (4) tempol + 1400 W. Cutaneous vasodilation was induced via local heating and NO-dependent vasodilation was quantified. At control sites, NO-dependent vasodilation was lower in non-Hispanic Black (45 ± 9% NO) relative to non-Hispanic White (79 ± 9% NO; p < 0.01; effect size, d = 3.78) participants. Tempol (62 ± 16% NO), 1400 W (78 ± 12% NO) and tempol +1400 W (80 ± 13% NO) increased NO-dependent vasodilation in non-Hispanic Black participants relative to control sites (all p < 0.01; d = 1.22, 3.05, 3.03, respectively). The effect of 1400 W (p = 0.04, d = 1.11) and tempol +1400 W (p = 0.03, d = 1.22) was greater than tempol in non-Hispanic Black participants. There was no difference between non-Hispanic Black and non-Hispanic White participants at 1400 W or tempol + 1400 W sites. These data suggest iNOS has a greater effect on NO-dependent vasodilation than superoxide in non-Hispanic Black participants.

Decreased role of neuropeptides in the microvascular function in migraine patients with polycystic ovary syndrome

BACKGROUND AND AIMS

To understand pathophysiological mechanisms underlying migraine as a cardiovascular risk factor, we studied neuropeptide action and endothelial function as measures of peripheral microvascular function in middle-aged women with or without migraine.

METHODS

We included women with the endocrine disorder polycystic ovary syndrome (PCOS), a population with supposed elevated cardiovascular risk, with and without comorbid migraine. In 26 women without and 23 women with migraine in the interictal phase (mean age 50.8 ± 2.9 years) local thermal hyperemia (LTH) of the skin of the volar forearm was measured cross-sectionally under control conditions, after inhibition of neuropeptide release by 5% lidocaine/prilocaine (EMLA) cream application, and after inhibition of nitric oxide formation by iontophoresis of NG-monomethyl-l-arginine (L-NMMA). Hereafter, changes in the natural logarithm of the reactive hyperemia index (lnRHI) and augmentation index (AI) during reperfusion after occlusion-derived ischemia were measured.

RESULTS

While mean values under control conditions and L-NMMA conditions were similar, migraine patients had a significantly higher mean area of the curve (AUC) of the total LTH response after EMLA application than those without (86.7 ± 26.5% versus 67.9 ± 24.2%; p = 0.014). This was also reflected by a higher median AUC of the plateau phase under similar conditions in women with migraine compared to those without (83.2% (IQR[73.2-109.5]) versus 73.2% (IQR[54.3-92.0]); p = 0.039). Mean changes in lnRHI and AI scores were similar in both groups.

CONCLUSIONS

In PCOS patients with migraine, neuropeptide action was lower compared with those without migraine. While larger studies are warranted, these findings provide a potential mechanism supporting previous findings that migraine may be independent from traditional risk factors, including atherosclerosis.

Skin microvascular reactivity in patients with diabetic retinopathy

AIMS

Early detection of microangiopathic complications of diabetes mellitus (DM) is necessary to analyze the patient's condition and prevent disease progression. The study was aimed to investigate the relationship between the presence of retinopathy and decreased reactivity of the microcirculatory bed in patients with diabetes.

METHODS

The study involved 130 subjects: healthy volunteers (n = 48), DM patients without retinopathy (n = 53) and with retinopathy (n = 29). Skin microvascular reactivity was assessed on the forearm using laser Doppler flowmetry with a local heating test combined with occlusion.

RESULTS

The slope of local thermal hyperemia curve (Slope-120) and other parameters of microvascular reactivity showed difference in pairwise comparisons between the groups. Slope-120 had the highest sensitivity (0.759) and specificity (0.717) in detection of diabetic retinopathy. The decrease of Slope-120 was associated with retinopathy (odds ratio (OR) - 8.3 (2.9-24.1), p < 0.001), even after adjusting for other factors (OR - 11.0 (1.6-77.2), p = 0.016).

CONCLUSIONS

Thus, assessment of skin microvascular reactivity may be a useful test for detecting signs of microangiopathic complications and for screening patients in risk group. Decreased microvascular reactivity has been shown to be prospective as an independent indicator of retinopathy in type 1 DM.

Endothelin A receptor inhibition increases nitric oxide-dependent vasodilation independent of superoxide in non-Hispanic Black young adults

Young non-Hispanic Black adults have reduced microvascular endothelial function compared with non-Hispanic White counterparts, but the mechanisms are not fully elucidated. The purpose of this study was to investigate the effect of endothelin-1 A receptor (ET_AR) and superoxide on cutaneous microvascular function in young non-Hispanic Black (n = 10) and White (n = 10) adults. Participants were instrumented with four intradermal microdialysis fibers: 1) lactated Ringer's (control), 2) 500 nM BQ-123 (ET_AR antagonist), 3) 10 μM tempol (superoxide dismutase mimetic), and 4) BQ-123 + tempol. Skin blood flow was assessed via laser-Doppler flowmetry (LDF), and each site underwent rapid local heating from 33°C to 39°C. At the plateau of local heating, 20 mM l-NAME [nitric oxide (NO) synthase inhibitor] was infused to quantify NO-dependent vasodilation. Data are means ± standard deviation. NO-dependent vasodilation was decreased in non-Hispanic Black compared with non-Hispanic White young adults (P < 0.01). NO-dependent vasodilation was increased at BQ-123 sites (73 ± 10% NO) and at BQ-123 + tempol sites (71 ± 10%NO) in non-Hispanic Black young adults compared with control (53 ± 13%NO, P = 0.01). Tempol alone had no effect on NO-dependent vasodilation in non-Hispanic Black young adults (63 ± 14%NO, P = 0.18). NO-dependent vasodilation at BQ-123 sites was not statistically different between non-Hispanic Black and White (80 ± 7%NO) young adults (P = 0.15). ET_AR contributes to reduced NO-dependent vasodilation in non-Hispanic Black young adults independent of superoxide, suggesting a greater effect on NO synthesis rather than NO scavenging via superoxide.NEW & NOTEWORTHY Endothelin-1 A receptors (ET_ARs) have been shown to reduce endothelial function independently and through increased production of superoxide. We show that independent ET_AR inhibition increases microvascular endothelial function in non-Hispanic Black young adults. However, administration of a superoxide dismutase mimetic alone and in combination with ET_AR inhibition had no effect on microvascular endothelial function suggesting that, in the cutaneous microvasculature, the negative effects of ET_AR in non-Hispanic Black young adults are independent of superoxide production.

Effects of biological sex and oral contraceptive pill use on cutaneous microvascular endothelial function and nitric oxide-dependent vasodilation in humans

The purpose of this study was to evaluate in vivo endothelial function and nitric oxide (NO)-dependent vasodilation between women in either menstrual or placebo pill phases of their respective hormonal exposure [either naturally cycling (NC) or using oral contraceptive pills (OCPs)] and men. A planned subgroup analysis was then completed to assess endothelial function and NO-dependent vasodilation between NC women, women using OCP, and men. Endothelium-dependent and NO-dependent vasodilation were assessed in the cutaneous microvasculature using laser-Doppler flowmetry, a rapid local heating protocol (39°C, 0.1 °C/s), and pharmacological perfusion through intradermal microdialysis fibers. Data are represented as means ± standard deviation. Men displayed greater endothelium-dependent vasodilation (plateau, men: 71 ± 16 vs. women: 52 ± 20%CVC_max, P < 0.01), but lower NO-dependent vasodilation (men: 52 ± 11 vs. women: 63 ± 17%NO, P = 0.05) compared with all women. Subgroup analysis revealed NC women had lower endothelium-dependent vasodilation (plateau, NC women: 48 ± 21%CVC_max, P = 0.01) but similar NO-dependent vasodilation (NC women: 52 ± 14%NO, P > 0.99), compared with men. Endothelium-dependent vasodilation did not differ between women using OCP and men (P = 0.12) or NC women (P = 0.64), but NO-dependent vasodilation was significantly greater in women using OCP (74 ± 11%NO) than both NC women and men (P < 0.01 for both). This study highlights the importance of directly quantifying NO-dependent vasodilation in cutaneous microvascular studies. This study also provides important implications for experimental design and data interpretation.NEW & NOTEWORTHY This study supports differences in microvascular endothelial function and nitric oxide (NO)-dependent vasodilation between women in low hormone phases of two hormonal exposures and men. However, when separated into subgroups of hormonal exposure, women during placebo pills of oral contraceptive pill (OCP) use have greater NO-dependent vasodilation than naturally cycling women in their menstrual phase and men. These data improve knowledge of sex differences and the effect of OCP use on microvascular endothelial function.

The peripheral vascular responses in non-freezing cold injury and matched controls

NEW FINDINGS

What is the central question of this study? Does non-freezing cold injury (NFCI) alter normal peripheral vascular function? What is the main finding and its importance? Individuals with NFCI were more cold sensitive (rewarmed more slowly and felt more discomfort) than controls. Vascular tests indicated that extremity endothelial function was preserved with NFCI and that sympathetic vasoconstrictor response might be reduced. The pathophysiology underpinning the cold sensitivity associated with NFCI thus remains to be identified.

ABSTRACT

The impact of non-freezing cold injury (NFCI) on peripheral vascular function was investigated. Individuals with NFCI (NFCI group) and closely matched controls with either similar (COLD group) or limited (CON group) previous cold exposure were compared (n = 16). Peripheral cutaneous vascular responses to deep inspiration (DI), occlusion (PORH), local cutaneous heating (LH) and iontophoresis of acetylcholine and sodium nitroprusside were investigated. The responses to a cold sensitivity test (CST) involving immersion of a foot in 15°C water for 2 min followed by spontaneous rewarming, and a foot cooling protocol (footplate cooled from 34°C to 15°C), were also examined. The vasoconstrictor response to DI was lower in NFCI compared to CON (toe: 73 (28)% vs. 91 (17)%; P = 0.003). The responses to PORH, LH and iontophoresis were not reduced compared to either COLD or CON. During the CST, toe skin temperature rewarmed more slowly in NFCI than COLD or CON (10 min: 27.4 (2.3)°C vs. 30.7 (3.7)°C and 31.7 (3.9)°C, P < 0.05, respectively); however, no differences were observed during the footplate cooling. NFCI were more cold-intolerant (P < 0.0001) and reported colder and more uncomfortable feet during the CST and footplate cooling than COLD and CON (P < 0.05). NFCI showed a decreased sensitivity to sympathetic vasoconstrictor activation than CON and greater cold sensitivity (CST) compared to COLD and CON. None of the other vascular function tests indicated endothelial dysfunction. However, NFCI perceived their extremities to be colder and more uncomfortable/painful than the controls.

Acute impact of aerobic exercise on local cutaneous thermal hyperaemia

Little is known about the acute changes in cutaneous microvascular function that occur in response to exercise, the accumulation of which may provide the basis for beneficial chronic cutaneous vascular adaptations. Therefore, we examined the effects of acute exercise on cutaneous thermal hyperaemia. Twelve healthy, recreationally active participants (11 male, 1 female) performed 30-minute cycling at 50 % (low-intensity exercise, LOW) or 75 % (high-intensity exercise, HIGH) maximum heart rate. Laser Doppler flowmetry (LDF) and rapid local skin heating were used to quantify cutaneous thermal hyperaemia before (PRE), immediately following (IMM) and 1-h (1HR) after exercise. Baseline, axon reflex peak, axon reflex nadir, plateau, maximum skin blood flow responses to rapid local heating (42 °C for 30-min followed by 44 °C for 15-min) at each stage were assessed and indexed as cutaneous vascular conductance [CVC = flux / mean arterial blood pressure (MAP), PU·mm Hg^-1], and expressed as a percentage of maximum (%CVC_max). Exercise increased heart rate (HR), MAP and skin blood flow (all P < 0.001), and to a greater extent during HIGH (all P < 0.001). The axon reflex peak and nadir were increased immediately and 1-h after exercise (all comparisons P < 0.01 vs. PRE), which did not differ between intensities (peak: P = 0.34, axon reflex nadir: P = 0.91). The endothelium-dependent plateau response was slightly elevated after exercise (P = 0.06), with no effect of intensity (P = 0.58) nor any interaction effect (P = 0.55). CONCLUSION: Exercise increases cutaneous microvascular axonal responses to local heating for up to 1-h, suggesting an augmented sensory afferent function post-exercise. Acute exercise may only modestly affect endothelial function in cutaneous microcirculation.

Habitual intake of dietary methylglyoxal is associated with less low-grade inflammation: the Maastricht Study

BACKGROUND

Dicarbonyls are major reactive precursors of advanced glycation endproducts (AGEs). Dicarbonyls are formed endogenously and also during food processing. Circulating dicarbonyls and AGEs are associated with inflammation and microvascular complications of diabetes, but for dicarbonyls from the diet these associations are currently unknown.

OBJECTIVES

We sought to examine the associations of dietary dicarbonyl intake with low-grade inflammation and microvascular function.

METHODS

In 2792 participants (mean ± SD age: 60 ± 8 y; 50% men; 26% type 2 diabetes) of the population-based cohort the Maastricht Study, we estimated the habitual intake of the dicarbonyls methylglyoxal (MGO), glyoxal (GO), and 3-deoxyglucosone (3-DG) by linking FFQ outcome data to our food composition database of the MGO, GO, and 3-DG content of >200 foods. Low-grade inflammation was assessed as six plasma biomarkers, which were compiled in a z score. Microvascular function was assessed as four plasma biomarkers, compiled in a zscore; as diameters and flicker light-induced dilation in retinal microvessels; as heat-induced skin hyperemic response; and as urinary albumin excretion. Cross-sectional associations of dietary dicarbonyls with low-grade inflammation and microvascular function were investigated using linear regression with adjustments for age, sex, potential confounders related to cardiometabolic risk factors, and lifestyle and dietary factors.

RESULTS

Fully adjusted analyses revealed that higher intake of MGO was associated with a lower z score for inflammation [standardized β coefficient (STD β): -0.05; 95% CI: -0.09 to -0.01, with strongest inverse associations for hsCRP and TNF-α: both -0.05; -0.10 to -0.01]. In contrast, higher dietary MGO intake was associated with impaired retinal venular dilation after full adjustment (STD β: -0.07; 95% CI: -0.12 to -0.01), but not with the other features of microvascular function. GO and 3-DG intakes were not consistently associated with any of the outcomes.

CONCLUSION

Higher habitual intake of MGO was associated with less low-grade inflammation. This novel, presumably beneficial, association is the first observation of an association between MGO intake and health outcomes in humans and warrants further investigation.

Pathogenic Mechanisms of Pulmonary Arterial Hypertension: Homeostasis Imbalance of Endothelium-Derived Relaxing and Contracting Factors

Pulmonary arterial hypertension (PAH) is a progressive and fatal disease. Sustained pulmonary vasoconstriction and concentric pulmonary vascular remodeling contribute to the elevated pulmonary vascular resistance and pulmonary artery pressure in PAH. Endothelial cells regulate vascular tension by producing endothelium-derived relaxing factors (EDRFs) and endothelium-derived contracting factors (EDCFs). Homeostasis of EDRF and EDCF production has been identified as a marker of the endothelium integrity. Impaired synthesis or release of EDRFs induces persistent vascular contraction and pulmonary artery remodeling, which subsequently leads to the development and progression of PAH. In this review, the authors summarize how EDRFs and EDCFs affect pulmonary vascular homeostasis, with special attention to the recently published novel mechanisms related to endothelial dysfunction in PAH and drugs associated with EDRFs and EDCFs.

Novel Method to Assess Endothelial Function via Monitoring of Perfusion Response to Local Heating by Imaging Photoplethysmography

Endothelial dysfunction is one of the most important markers of the risk of cardiovascular complications. This study is aimed to demonstrate the feasibility of imaging photoplethysmography to assess microcirculation response to local heating in order to develop a novel technology for assessing endothelial function. As a measure of vasodilation, we used the relative dynamics of the pulsatile component of the photoplethysmographic waveform, which was assessed in a large area of the outer surface of the middle third of the subject's forearm. The perfusion response was evaluated in six healthy volunteers during a test with local skin heating up to 40-42 °C and subsequent relaxation. The proposed method is featured by accurate control of the parameters affecting the microcirculation during the prolonged study. It was found that in response to local hyperthermia, a multiple increase in the pulsation component, which has a biphasic character, was observed. The amplitude of the first phase of the perfusion reaction depends on both the initial skin temperature and the difference between the basal and heating temperatures. The proposed method allows the assessment of a reproducible perfusion increase in response to hyperthermia developed due to humoral factors associated with the endothelium, thus allowing detection of its dysfunction.

Remote ischaemic preconditioning - translating cardiovascular benefits to humans

Remote ischaemic preconditioning (RIPC), induced by intermittent periods of limb ischaemia and reperfusion, confers cardiac and vascular protection from subsequent ischaemia–reperfusion (IR) injury. Early animal studies reliably demonstrate that RIPC attenuated infarct size and preserved cardiac tissue. However, translating these adaptations to clinical practice in humans has been challenging. Large clinical studies have found inconsistent results with respect to RIPC eliciting IR injury protection or improving clinical outcomes. Follow‐up studies have implicated several factors that potentially affect the efficacy of RIPC in humans such as age, fitness, frequency, disease state and interactions with medications. Thus, realizing the clinical potential for RIPC may require a human experimental model where confounding factors are more effectively controlled and underlying mechanisms can be further elucidated. In this review, we highlight recent experimental findings in the peripheral circulation that have added valuable insight on the mechanisms and clinical benefit of RIPC in humans. Central to this discussion is the critical role of timing (i.e. immediate vs. delayed effects following a single bout of RIPC) and the frequency of RIPC. Limited evidence in humans has demonstrated that repeated bouts of RIPC over several days uniquely improves vascular function beyond that observed with a single bout alone. Since changes in resistance vessel and microvascular function often precede symptoms and diagnosis of cardiovascular disease, repeated bouts of RIPC may be promising as a preclinical intervention to prevent or delay cardiovascular disease progression.

Utilisation of skin blood flow as a precursor for pressure injury development in persons with acute spinal cord injury: A proof of concept

People with spinal cord injury (SCI) are at high risk of developing a pressure injury. It is unclear why some people with SCI develop pressure injury while others with similar predisposing risk factors do not during acute hospitalisation. This may hinder healthcare utilisation to prevent pressure injuries. The purpose of the study was to examine the proof-of-concept objective bedside skin blood flow measurements before a pressure injury develops in spinal cord injured patients during acute hospitalisation. This was an observational study. All participants had acute traumatic SCI and were pressure injury-free upon enrollment. Skin blood flow patterns were collected at both heels under two circumstances: localised pressure for reactive hyperemia, and localised heating for heat hyperemia. Our results showed that reactive and heat hyperemia were successfully induced in all eleven participants. Two participants developed pressure injury and nine did not have pressure injury at discharge. Heat hyperemia was smaller in participants with pressure injury. No difference was observed in reactive hyperemia between the groups. In conclusion, skin blood flow measurements could be obtained at bedside during acute hospitalisation of SCI for the purpose of research. Further examination of a larger group is warranted to determine clinical use of heat hyperemia pattern as predictor for pressure injury development.

Delayed Cutaneous Microvascular Responses With Non-consecutive 3 Days of Remote Ischemic Preconditioning

The optimal frequency and duration of remote ischemic preconditioning (RIPC) that augments microvascular function is unknown. A single bout of RIPC increases cutaneous endothelial function for ∼48 h, whereas 1 week of daily RIPC bouts improves more sustained endothelium-independent function. We hypothesized that 3 days of RIPC separated by rest days (3QOD RIPC) would result in sustained increases in both endothelium-dependent and endothelium-independent functions. Cutaneous microvascular function was assessed in 13 healthy young participants (aged 20.5 ± 3.9 years; 5 males, 8 females) before 3QOD and then 24, 48, and 72 h and a week after 3QOD. RIPC consisted of four repetitions of 5 min of blood flow occlusion separated by 5 min of reperfusion. Skin blood flow responses to local heating (T_loc = 42°C), acetylcholine (Ach), and sodium nitroprusside (SNP) were measured using laser speckle contrast imaging and expressed as cutaneous vascular conductance (CVC = PU⋅mmHg^–1). Local heating-mediated vasodilation was increased 72 h after 3QOD and the increased responsivity persisted a week later (1.08 ± 0.24 vs. 1.34 ± 0.46, 1.21 ± 0.36 PU⋅mmHg^–1; ΔCVC, pre-RIPC vs. 72 h, a week after 3QOD; P = 0.054). Ach-induced cutaneous vasodilation increased a week after 3QOD (0.73 ± 0.41 vs. 0.95 ± 0.49 PU⋅mmHg^–1; ΔCVC, pre-RIPC vs. a week after 3QOD; P < 0.05). SNP-induced cutaneous vasodilation increased 24 h after 3QOD (0.47 ± 0.28 vs. 0.63 ± 0.35 PU⋅mmHg^–1; ΔCVC, pre-RIPC vs. 24 h; P < 0.05), but this change did not persist thereafter. Thus, 3QOD induced sustained improvement in endothelium-dependent vasodilation but was not sufficient to sustain increases in endothelium-independent vasodilation.

Women with a history of preeclampsia have preserved sensory nerve-mediated dilatation in the cutaneous microvasculature

NEW FINDINGS

What is the central question of this study? Are sensory nerve-mediated vasodilatation and the NO-dependent contribution to that response attenuated in the cutaneous microvasculature of women who have had preeclampsia? What is the main finding and its importance? Women who have had preeclampsia demonstrate attenuated microvascular endothelium-dependent dilatation compared to women with a history of uncomplicated pregnancy. However, there are no differences in sensory nerve-mediated vasodilatation between groups. This suggests that the neurogenic response is not altered following preeclampsia, and that the NO-dependent vasodilatation of the neurogenic response is not related to endothelium-dependent NO-mediated dilatation in these women.

ABSTRACT

Women who have had preeclampsia (PE) demonstrate microvascular endothelial dysfunction, mediated in part by reduced nitric oxide (NO)-dependent mechanisms. Localized heating of the skin induces a biphasic vasodilatation response: a sensory nerve-mediated initial peak, followed by a sustained endothelium-dependent plateau. We have previously shown that the endothelium-dependent plateau is attenuated in PE. However, it is unknown if the sensory nerve-mediated initial peak is similarly attenuated. Therefore, the purpose of this study was to examine the effect of PE history on sensory nerve-mediated vasodilatation and the NO-dependent contribution to that response. We hypothesized that PE would have an attenuated initial peak and a reduced NO-dependent contribution to that response compared to women with a history of normotensive pregnancy (healthy controls, HC). Nine HC (31 ± 4 years) and nine PE (28 ± 6 years) underwent a standard local heating protocol (42°C; 0.1°C s^-1 ). Two intradermal microdialysis fibres were placed in the skin of the ventral forearm for the continuous local delivery of lactated Ringer solution alone (control) or 15-mM N^G -nitro-l-arginine methyl ester for nitric oxide synthase (NOS) inhibition. Red blood cell flux was measured at each site by laser Doppler flowmetry (LDF). Cutaneous vascular conductance was calculated (CVC = LDF/mean arterial pressure) and normalized to maximum (%CVC_max ; 28-mM SNP + local heat 43°C). There were no differences in the initial peak between groups (HC: 79 ± 8 vs. PE: 80 ± 10%CVC_max ; P = 0.936). NOS inhibition attenuated the initial peak in both HC (57 ± 18% CVC_max ; P = 0.003) and PE (54 ± 10%CVC_max ; P = 0.002). However, there were no differences in the NO-dependent portion of the initial peak (HC: 23 ± 16 vs. PE: 24 ± 9%; P = 0.777). The local heating plateau (HC: 99 ± 4 vs. PE: 88 ± 7%CVC_max ; P = 0.001) and NO contribution to the plateau (HC: 31 ± 9 vs. PE: 17 ± 14%; P = 0.02) were attenuated in PE. There was no relation between NO-dependent dilatation in the initial peak and NO-dependent dilatation in the plateau across groups (R²  = 0.005; P = 0.943). Women who have had PE demonstrate attenuated microvascular endothelium-dependent dilatation. However, there are no differences in sensory nerve-mediated vasodilatation following PE, suggesting that the NO-dependent vasodilatation of the neurogenic response is not related to endothelium-dependent NO-mediated dilatation in these women.

TRPA1 channel activation with cinnamaldehyde induces cutaneous vasodilation through NOS, but not COX and KCa channel, mechanisms in humans

ABSTRACT

Transient receptor potential ankyrin 1 (TRPA1) channel activation induces cutaneous vasodilation in humans in vivo. However, the mechanisms underlying this response remains equivocal. We hypothesized that nitric oxide (NO) synthase (NOS) and Ca2+ activated K+ (KCa) channels contribute to the TRPA1 channel-induced cutaneous vasodilation with no involvement of cyclooxygenase (COX). Cutaneous vascular conductance (CVC) in 9 healthy young adults was assessed at four dorsal forearm skin sites treated by intradermal microdialysis with either: 1) vehicle control (98% propylene glycol + 1.985% dimethyl sulfoxide + 0.015% lactated Ringer solution), 2) 10 mM L-NAME, a non-selective NOS inhibitor, 3) 10 mM ketorolac, a non-selective COX inhibitor, or 4) 50 mM tetraethylammonium, a non-selective KCa channel blocker. Cinnamaldehyde, a TRPA1 channel activator, was administered to each skin site in a dose-dependent manner (2.9, 8.8, 26 and 80 %, each lasting ≥30min). Administration of ≥8.8% cinnamaldehyde increased CVC from baseline at the vehicle control site by as much as 27.4% [95 % confidence interval of 5.3] (P<0.001). NOS inhibitor attenuated the cinnamaldehyde induced-increases in CVC at the 8.8, 26.0, and 80.0% concentrations relative to the vehicle control site (all P≤0.05). In contrast, both the COX inhibitor and KCa channel blockers did not attenuate the cinnamaldehyde induced-increases in CVC relative to the vehicle control site for all concentrations (all P≥0.130). We conclude that in human skin in vivo, NOS plays a role in modulating the regulation of cutaneous vasodilation in response to TRPA1 channel activation with no detectable contributions of COX and KCa channels.

Na+-K+-ATPase plays a major role in mediating cutaneous thermal hyperemia achieved by local skin heating to 39°C

Na⁺-K⁺-ATPase is integrally involved in mediating cutaneous vasodilation during an exercise-heat stress, which includes an interactive role with nitric oxide synthase (NOS). Here, we assessed if Na⁺-K⁺-ATPase also contributes to cutaneous thermal hyperemia induced by local skin heating, which is commonly used to assess cutaneous endothelium-dependent vasodilation. Furthermore, we assessed the extent to which NOS contributes to this response. Cutaneous vascular conductance (CVC) was measured continuously at four forearm skin sites in 11 young adults (4 women). After baseline measurement, local skin temperature was increased from 33°C to 39°C to induce cutaneous thermal hyperemia. Once a plateau in CVC was achieved, each skin site was continuously perfused via intradermal microdialysis with either: 1) lactated Ringer solution (control), 2) 6 mM ouabain, a Na⁺-K⁺-ATPase inhibitor, 3) 20 mM l-NAME, a NOS inhibitor, or 4) a combination of both. Relative to the control site, CVC during the plateau phase of cutaneous thermal hyperemia (∼50% max) was reduced by the lone inhibition of Na⁺-K⁺-ATPase (-19 ± 8% max, P = 0.038) and NOS (-32 ± 4% max, P < 0.001), as well as the combined inhibition of both (-37 ± 9% max, P < 0.001). The magnitude of reduction was similar between NOS inhibition alone and combined inhibition (P = 1.000). The administration of both Na⁺-K⁺-ATPase and NOS inhibitors fully abolished the plateau of CVC with values returning to preheating baseline values (P = 0.439). We show that Na⁺-K⁺-ATPase contributes to cutaneous thermal hyperemia during local skin heating to 39°C, and this response is partially mediated by NOS.NEW & NOTEWORTHY Cutaneous thermal hyperemia during local skin heating to 39°C, which is highly dependent on nitric oxide synthase (NOS), is frequently used to assess endothelium-dependent cutaneous vasodilation. We showed that Na⁺-K⁺-ATPase mediates the regulation of cutaneous thermal hyperemia partly via NOS-dependent mechanisms although a component of the Na⁺-K⁺-ATPase modulation of cutaneous thermal hyperemia is NOS independent. Thus, as with NOS, Na⁺-K⁺-ATPase may be important in the regulation of cutaneous endothelial vascular function.

Habitual intake of dietary advanced glycation end products is not associated with generalized microvascular function-the Maastricht Study

BACKGROUND

Endogenously formed advanced glycation end products (AGEs) may be important drivers of microvascular dysfunction and the microvascular complications of diabetes. AGEs are also formed in food products, especially during preparation methods involving dry heat.

OBJECTIVES

We aimed to assess cross-sectional associations between dietary AGE intake and generalized microvascular function in a population-based cohort.

METHODS

In 3144 participants of the Maastricht Study (mean ± SD age: 60 ± 8 y, 51% men) the dietary AGEs Nε-(carboxymethyl)lysine (CML), Nε-(1-carboxyethyl)lysine (CEL), and Nδ-(5-hydro-5-methyl-4-imidazolon-2-yl)-ornithine (MG-H1) were estimated using the combination of our ultra-performance LC-tandem MS dietary AGE database and an FFQ. Microvascular function was determined in the retina as flicker light-induced arteriolar and venular dilation and as central retinal arteriolar and venular equivalents, in plasma as a z score of endothelial dysfunction biomarkers (soluble vascular adhesion molecule 1 and soluble intracellular adhesion molecule 1, soluble E-selectin, and von Willebrand factor), in skin as the heat-induced skin hyperemic response, and in urine as 24-h albuminuria. Associations were evaluated using multiple linear regression adjusting for demographic, cardiovascular, lifestyle, and dietary factors.

RESULTS

Overall, intakes of CML, CEL, and MG-H1 were not associated with the microvascular outcomes. Although higher intake of CEL was associated with higher flicker light-induced venular dilation (β percentage change over baseline: 0.14; 95% CI: 0.02, 0.26) and lower plasma biomarker z score (β: -0.04 SD; 95% CI: -0.08, -0.00 SD), the effect sizes were small and their biological relevance can be questioned.

CONCLUSIONS

We did not show any strong association between habitual intake of dietary AGEs and generalized microvascular function. The contribution of dietary AGEs to generalized microvascular function should be further assessed in randomized controlled trials using specifically designed dietary interventions.

Regional cutaneous vasodilator responses to rapid and gradual local heating in young adults

PURPOSE

To examine the extent of regional variations in cutaneous vasodilatation during rapid and gradual local thermal hyperaemia (LTH) in young adults.

METHODS

In thirty young adults (21 ± 3 years, 15 females), cutaneous vascular conductance, normalized to maximum local skin heating at 44 °C (%CVC_max), was assessed at the upper chest, abdomen, dorsal arm, dorsal forearm, thigh, and medial calf during rapid (33-42 °C at 1 °C·20 s^-1) and gradual (33-42 °C at 1 °C·5 min^-1) LTH on separate days. For both protocols, local temperatures were held at 42 °C for up to 35 min, followed by 20-30 min at 44 °C. During rapid LTH, between-region responses were evaluated at baseline, the initial vasodilator peak, and 42 °C plateau. During gradual LTH, responses were assessed at baseline and the 42 °C plateau.

RESULTS

There were significant main effects of body region on %CVC_max for the initial peak and plateau during rapid LTH and for the plateau during gradual LTH (all P < 0.001) Conversely, main effects of sex and the sex by region interaction were not significant (all P > 0.05). The magnitudes of between-region differences varied across the body (~1-17% range). The greatest effects were observed for the abdomen, wherein responses were consistently lower compared to other regions. Further, responses were consistent between males and females across all body regions and heating phases.

CONCLUSION

Regional variations in the cutaneous vasodilator response to local heating are evident for rapid and gradual LTH in young adults, with the largest effects observed for the abdomen, albeit regional differences were similar between sexes.

Assessment and pathophysiology of microvascular disease: recent progress and clinical implications

The development of novel, non-invasive techniques and standardization of protocols to assess microvascular dysfunction have elucidated the key role of microvascular changes in the evolution of cardiovascular (CV) damage, and their capacity to predict an increased risk of adverse events. These technical advances parallel with the development of novel biological assays that enabled the ex vivo identification of pathways promoting microvascular dysfunction, providing novel potential treatment targets for preventing cerebral-CV disease. In this article, we provide an update of diagnostic testing strategies to detect and characterize microvascular dysfunction and suggestions on how to standardize and maximize the information obtained from each microvascular assay. We examine emerging data highlighting the significance of microvascular dysfunction in the development CV disease manifestations. Finally, we summarize the pathophysiology of microvascular dysfunction emphasizing the role of oxidative stress and its regulation by epigenetic mechanisms, which might represent potential targets for novel interventions beyond conventional approaches, representing a new frontier in CV disease reduction.

Regional variation in nitric oxide-dependent cutaneous vasodilatation during local heating in young adults

NEW FINDINGS

What is the central question of this study? Are regional differences in nitric oxide (NO)-dependent cutaneous vasodilatation during local skin heating present in young adults? What is the main finding and its importance? NO-dependent cutaneous vasodilatation varied across the body. The abdomen demonstrated larger NO contributions, while the chest demonstrated smaller NO contributions, compared to other regions. This exploratory work is an important first step in characterizing regional heterogeneity of cutaneous microvascular control across the torso and limbs. Equally, it serves to generate hypotheses for future studies examining regional cutaneous microvascular control in ageing and disease.

ABSTRACT

Regional variations in cutaneous vasodilatation during local skin heating exist across the body. While nitric oxide (NO) is a well-known modulator of this response, the extent of regional differences in NO-dependent cutaneous vasodilatation during local skin heating remains uncertain. In 16 habitually active young adults (8 females; 25 ± 5 years), cutaneous vascular conductance, normalized to maximum vasodilatation (% CVC_max ), was assessed at the upper chest, abdomen, dorsal forearm, thigh and lateral calf during local skin heating. Across all regions, local skin temperatures were simultaneously increased from 33 to 42°C (1°C per 10 s), and held until a stable heating plateau was achieved (∼40 min). Next, with local skin temperature maintained at 42°C, 20 mM of N^G -nitro-l-arginine methyl ester (l-NAME) was continuously infused at each site until a stable l-NAME plateau was achieved (∼40 min). The difference between heating and l-NAME plateaus was identified as the NO contribution for each region. There was no evidence for region-specific responses at baseline (P = 0.561), the heating plateau (P = 0.351) or l-NAME plateau (P = 0.082), but there was for the NO contribution (P = 0.048). Overall, point estimates for between-region differences in the NO contribution varied across the body from 0 to 19% CVC_max . The greatest effects were observed for the abdomen, wherein the NO contribution was consistently greater than for the other regions (range: 9-19% CVC_max ). The chest was consistently lower than the other regions (range: 7-19% CVC_max ). The smallest effects were observed between limb regions (range: 0-2% CVC_max ). These findings advance our understanding of the mechanisms influencing regional variations in the cutaneous vasodilator response to local skin heating in young adults.

Hydrogen Sulfide in Skin Diseases: A Novel Mediator and Therapeutic Target

Together with nitric oxide (NO) and carbon monoxide (CO), hydrogen sulfide (H₂S) is now recognized as a vital gaseous transmitter. The ubiquitous distributions of H₂S-producing enzymes and potent chemical reactivities of H₂S in biological systems make H₂S unique in its ability to regulate cellular and organ functions in both health and disease. Acting as an antioxidant, H₂S can combat oxidative species such as reactive oxygen species (ROS) and reactive nitrogen species (RNS) and protect the skin from oxidative stress. The aberrant metabolism of H₂S is involved in the pathogenesis of several skin diseases, such as vascular disorders, psoriasis, ulcers, pigment disorders, and melanoma. Furthermore, H₂S donors and some H₂S hybrids have been evaluated in many experimental models of human disease and have shown promising therapeutic results. In this review, we discuss recent advances in understanding H₂S and its antioxidant effects on skin pathology, the roles of altered H₂S metabolism in skin disorders, and the potential value of H₂S as a therapeutic intervention in skin diseases.

Delayed window of improvements in skin microvascular function following a single bout of remote ischaemic preconditioning

NEW FINDINGS

What is the central question of this study? Animal infarct studies indicate a delayed window of cardiac protection after remote ischaemic preconditioning (RIPC); however, the presence and duration of this delayed effect have not been examined in human microvasculature in vivo. What is the main finding and its importance? Cutaneous vasodilatation induced by local heating or ACh was increased significantly 24 and 48 h after a single bout of RIPC, respectively. Neither response persisted beyond ∼48 h. Sodium nitroprusside-induced cutaneous vasodilatation was not altered. These findings reveal a delayed increase in microvascular endothelial function after a single bout of RIPC.

ABSTRACT

Remote ischaemic preconditioning (RIPC) induces protective effects from ischaemia-reperfusion injury. In the myocardium and conduit vasculature, a single bout of RIPC confers delayed protection that begins 24 h afterwards and lasts for 2-3 days. However, the extent and the time line in which a single bout of RIPC affects the human microvasculature are unclear. We hypothesized that a single bout of RIPC results in a delayed increase in skin microvascular function. Sixteen healthy participants (age, 23 ± 4 years; seven males, nine females; MAP, 82 ± 7 mmHg) were recruited to measure cutaneous microvascular function immediately before a single bout of RIPC and 24, 48 and 72 h and 1 week after the bout. The RIPC consisted of four repetitions of 5 min of arm blood flow occlusion interspersed by 5 min reperfusion. Skin blood flow responses to local heating (local temperature of 42°C), ACh and sodium nitroprusside were measured by laser speckle contrast imaging and expressed as the cutaneous vascular conductance (CVC; in perfusion units per millimetre of mercury). Vasodilatation in response to local heating was increased 24 and 48 h after RIPC (ΔCVC, 1.05 ± 0.07 vs. 1.18 ± 0.07 and 1.24 ± 0.08 PU mmHg^-1 , pre- vs. 24 and 48 h post-RIPC; P < 0.05). Acetylcholine-induced cutaneous vasodilatation increased significantly 48 h after RIPC (ΔCVC, 0.71 ± 0.07 vs. 0.93 ± 0.12 PU mmHg^-1 , pre- vs. 48 h post-RIPC; P < 0.05) and returned to baseline thereafter. Sodium nitroprusside-mediated vasodilatation did not change. Thus, a single bout of RIPC elicited a delayed response in the microvasculature, resulting in an improvement in the endothelium-dependent cutaneous vasodilatory response that peaked ∼48 h post-RIPC.

Effects of short-term heat acclimation on whole-body heat exchange and local nitric oxide synthase- and cyclooxygenase-dependent heat loss responses in exercising older men

NEW FINDINGS

What is the central question of this study? Does short-term heat acclimation enhance whole-body evaporative heat loss and augment nitric oxide synthase (NOS)-dependent cutaneous vasodilatation and NOS- and cyclooxygenase (COX)-dependent sweating, in exercising older men? What is the main finding and its importance? Our preliminary data (n = 8) demonstrated that short-term heat acclimation improved whole-body evaporative heat loss, but it did not influence the effects of NOS and/or COX inhibition on cutaneous vasodilatation or sweating in older men during an exercise-heat stress. These outcomes might imply that although short-term heat acclimation enhances heat dissipation in older men, it does not modulate NOS- and COX-dependent control of cutaneous vasodilatation or sweating on the forearm.

ABSTRACT

Ageing is associated with decrements in whole-body heat loss (evaporative + dry heat exchange), which might stem from alterations in nitric oxide synthase (NOS)- and cyclooxygenase (COX)-dependent cutaneous vasodilatation and sweating. We evaluated whether short-term heat acclimation would (i) enhance whole-body heat loss primarily by increasing evaporative heat loss, and (ii) augment NOS-dependent cutaneous vasodilatation and NOS- and COX-dependent sweating, in exercising older men. Eight older men [mean (SD) age, 59 (8) years] completed a calorimetry and microdialysis trial before and after 7 days of exercise-heat acclimation. For the calorimetry trials, whole-body evaporative and dry heat exchange were assessed using direct calorimetry during 30 min bouts of cycling at light, moderate and vigorous metabolic heat productions (150, 200 and 250 W/m² , respectively) in dry heat (40°C, 20% relative humidity). For the microdialysis trials, local cutaneous vascular conductance and sweat rate were assessed during 60 min exercise in the heat (35°C, 20% relative humidity) at four dorsal forearm skin sites treated with lactated Ringer solution (control), NOS inhibitor, COX inhibitor or combined NOS and COX inhibitors, via microdialysis. Evaporative heat loss during moderate (P = 0.036) and vigorous (P = 0.021) exercise increased after acclimation. Inhibition of NOS alone reduced cutaneous vascular conductance to a similar extent before and after acclimation (P < 0.040), whereas separate and combined NOS and COX inhibition had no significant effects on sweating relative to the control site (P = 0.745). Our preliminary results might suggest that short-term heat acclimation improves evaporative heat loss, but does not significantly modulate the contributions of NOS or COX to cutaneous vasodilatation or sweating on the forearm in older men during an exercise-heat stress.

Inhibition of iNOS augments cutaneous endothelial NO-dependent vasodilation in prehypertensive non-Hispanic Whites and in non-Hispanic Blacks

We tested the hypothesis that inducible nitric oxide synthase (iNOS) contributes to reduced nitric oxide (NO)-dependent vasodilation in non-Hispanic Blacks and prehypertensive non-Hispanic Whites. Twenty Black and twenty White participants (10 normotensive, 10 prehypertensive per group; n = 40 total) participated in this study. Participants were instrumented with two microdialysis fibers, and each site was randomized as control (lactated Ringer) or iNOS inhibition (0.1 mM 1400W). Laser-Doppler flow probes and local heaters were used to measure skin blood flow and heat the skin to induce vasodilation, respectively. Each site was heated from 33°C to 39°C (rate: 0.1°C/s). Once a plateau was established, 20 mM nitro-l-arginine methyl ester (l-NAME), a nonspecific NOS inhibitor, was infused at each site to quantify NO-dependent vasodilation. At control sites, %NO-dependent vasodilation was reduced in prehypertensive Whites (47 ± 10%NO) and in both normotensive and prehypertensive Blacks (39 ± 9%NO and 28 ± 5%NO, respectively) relative to normotensive Whites (73 ± 8%NO; P < 0.0001 for all comparisons). Compared with respective control sites, iNOS inhibition increased NO-dependent vasodilation in prehypertensive Whites (68 ± 8%NO) and in both normotensive and prehypertensive Blacks (78 ± 8%NO and 55 ± 6%NO, respectively; P < 0.0001 for all comparisons). We failed to find an effect for normotensive Whites (77 ± 7%NO). After iNOS inhibition, %NO-dependent vasodilation was similar between normotensive Whites, prehypertensive Whites, and normotensive Blacks. Inhibition of iNOS increased NO-dependent vasodilation to a lesser extent in prehypertensive Blacks. These data suggest that iNOS contributes to reduced NO-dependent vasodilation in prehypertension and in Black participants.NEW & NOTEWORTHY Inducible nitric oxide synthase (iNOS) is typically upregulated in conditions of increased oxidative stress and may have detrimental effects on the vasculature. Endothelial nitric oxide (NO), which is cardioprotective, is reduced in prehypertensive non-Hispanic Whites and in non-Hispanic Blacks. We found that inhibition of iNOS can increase endothelial NO-dependent vasodilation in prehypertensive White participants and in both normotensive and prehypertensive Black participants.Inducible nitric oxide (NO) synthase (iNOS) can be upregulated under conditions of increased oxidative stress and may have detrimental effects on the vasculature. Endothelial NO, which is cardioprotective, is reduced in prehypertensive non-Hispanic Whites and in non-Hispanic Blacks. We found that inhibition of iNOS can increase endothelial NO-dependent vasodilation in prehypertensive White participants and in both normotensive and prehypertensive Black participants.

TRPV4 channel blockade does not modulate skin vasodilation and sweating during hyperthermia or cutaneous postocclusive reactive and thermal hyperemia

Transient receptor potential vanilloid 4 (TRPV4) channels exist on vascular endothelial cells and eccrine sweat gland secretory cells in human skin. Here, we assessed whether TRPV4 channels contribute to cutaneous vasodilation and sweating during whole body passive heat stress (protocol 1) and to cutaneous vasodilation during postocclusive reactive hyperemia and local thermal hyperemia (protocol 2). Intradermal microdialysis was employed to locally deliver pharmacological agents to forearm skin sites, where cutaneous vascular conductance (CVC) and sweat rate were assessed. In protocol 1 (12 young adults), CVC and sweat rate were increased by passive whole body heating, resulting in a body core temperature elevation of 1.2 ± 0.1°C. The elevated CVC and sweat rate assessed at sites treated with TRPV4 channel antagonist (either 200 µM HC-067047 or 125 µM GSK2193874) were not different from the vehicle control site (5% dimethyl sulfoxide). After whole body heating, the TRPV4 channel agonist (100 µM GSK1016790A) was administered to each skin site, eliciting elevations in CVC. Relative to control, this response was partly attenuated by both TRPV4 channel antagonists, confirming drug efficacy. In protocol 2 (10 young adults), CVC was increased following a 5-min arterial occlusion and during local heating from 33 to 42°C. These responses did not differ between the control and the TRPV4 channel antagonist sites (200 µM HC-067047). We show that TRPV4 channels are not required for regulating cutaneous vasodilation or sweating during a whole body passive heat stress. Furthermore, they are not required for regulating cutaneous vasodilation during postocclusive reactive hyperemia and local thermal hyperemia.

Sensory nerve-mediated and nitric oxide-dependent cutaneous vasodilation in normotensive and prehypertensive non-Hispanic blacks and whites

The purpose of this study was to investigate the effect of race and subclinical elevations in blood pressure (i.e., prehypertension) on cutaneous sensory nerve-mediated and nitric oxide (NO)-dependent vasodilation. We recruited participants who self-identified as either non-Hispanic black (n = 16) or non-Hispanic white (n = 16). Within each group, participants were subdivided as either normotensive (n = 8 per group) or prehypertensive (n = 8 per group). Each participant was instrumented with four intradermal microdialysis fibers: 1) control (lactated Ringer's), 2) 5% lidocaine (sensory nerve inhibition), 3) 20 mM N^ω-nitro-l-arginine methyl ester (l-NAME) (NO synthase inhibition), and 4) lidocaine + l-NAME. Skin blood flow was assessed via laser-Doppler flowmetry, and each site underwent local heating from 33°C to 39°C. At the plateau, 20 mM l-NAME were infused at control and lidocaine sites to quantify NO-dependent vasodilation. Maximal vasodilation was induced via 54 mM sodium nitroprusside and local heating to 43°C. Data are means ± SD. Sensory nerve-mediated cutaneous vasodilation was reduced in prehypertensive non-Hispanic white (34 ± 7%) and both non-Hispanic black groups (normotensive, 20 ± 9%, prehypertensive, 24 ± 15%) relative to normotensive non-Hispanic whites (54 ± 12%). NO-dependent vasodilation was also reduced in prehypertensive non-Hispanic white (41 ± 7%) and both non-Hispanic black groups (normotensive, 44 ± 7%, prehypertensive, 19 ± 7%) relative to normotensive non-Hispanic whites (60 ± 11%). The decrease in NO-dependent vasodilation in prehypertensive non-Hispanic blacks was further reduced relative to all other groups. These data suggest subclinical increases in blood pressure adversely affect sensory-mediated and NO-dependent vasodilation in both non-Hispanic blacks and whites.NEW & NOTEWORTHY Overt hypertension is known to reduce cutaneous sensory nerve-mediated and nitric oxide (NO)-dependent vasodilation, but the effect of subclinical increases in blood pressure (i.e., prehypertension) is unknown. The combined effect of race and prehypertension is also unknown. In this study, we found that prehypertension reduces cutaneous sensory nerve-mediated and NO-dependent vasodilation in both non-Hispanic white and black populations, with the greatest reductions observed in prehypertensive non-Hispanic blacks.

NO-mediated activation of KATP channels contributes to cutaneous thermal hyperemia in young adults

Local skin heating to 42°C causes cutaneous thermal hyperemia largely via nitric oxide (NO) synthase (NOS)-related mechanisms. We assessed the hypothesis that ATP-sensitive K⁺ (K_ATP) channels interact with NOS to mediate cutaneous thermal hyperemia. In 13 young adults (6 women, 7 men), cutaneous vascular conductance (CVC) was measured at four intradermal microdialysis sites that were continuously perfused with 1) lactated Ringer solution (control), 2) 5 mM glibenclamide (K_ATP channel blocker), 3) 20 mM N^G-nitro-l-arginine methyl ester (NOS inhibitor), or 4) a combination of K_ATP channel blocker and NOS inhibitor. Local skin heating to 42°C was administered at all four treatment sites to elicit cutaneous thermal hyperemia. Thirty minutes after the local heating, 1.25 mM pinacidil (K_ATP channel opener) and subsequently 25 mM sodium nitroprusside (NO donor) were administered to three of the four sites (each 25-30 min). The local heating-induced prolonged elevation in CVC was attenuated by glibenclamide (19%), but the transient initial peak was not. However, glibenclamide had no effect on the prolonged elevation in CVC in the presence of NOS inhibition. Pinacidil caused an elevation in CVC, but this response was abolished at the glibenclamide-treated skin site, demonstrating its effectiveness as a K_ATP channel blocker. The pinacidil-induced increase in CVC was unaffected by NOS inhibition, whereas the increase in CVC elicited by sodium nitroprusside was partly (15%) inhibited by glibenclamide. In summary, we showed an interactive effect of K_ATP channels and NOS for the plateau of cutaneous thermal hyperemia. This interplay may reflect a vascular smooth muscle cell K_ATP channel activation by NO.

Improved endothelial-dependent and endothelial-independent skin vasodilator responses following remote ischemic preconditioning

One week of daily remote ischemic preconditioning (RIPC) improves cutaneous vasodilatory (VD) function. However, the underlying mechanisms and the number of sessions needed to optimize this adaptive response remain unclear. We hypothesized that the responses to localized heating of the skin will be greater after 2 wk as opposed to 1 wk of RIPC. Furthermore, 2 wk of repeated RIPC will augment cutaneous VD responses to thermal and pharmacological stimuli. In methods, twenty-four participants (24 ± 2 yr; 13 men, 11 women) performed repeated RIPC (7 daily sessions over 1 wk, n = 11; 12 sessions over 2 wk, n = 13), consisting of four repetitions of 5 min of arm blood flow occlusion separated by 5 min reperfusion. Laser speckle contrast imaging was used to measure skin blood flow responses, in perfusion units (PU), to local heating (T_loc = 42°C), acetylcholine (ACh), and sodium nitroprusside (SNP) before and after repeated RIPC. Data were expressed as cutaneous vascular conductance (CVC, in PU/mmHg). In results, the VD response to local heating increased after RIPC (∆CVC from baseline; 1 wk: 0.94 ± 0.11 to 1.19 ± 0.15, 2 wk: 1.18 ± 0.07 to 1.33 ± 0.10 PU/mmHg; P < 0.05) but the ∆CVC did not differ between weeks. SNP-induced VD increased after 2 wk of RIPC (∆CVC; 0.34 ± 0.07 to 0.63 ± 0.11 PU/mmHg; P < 0.05), but ACh-induced VD did not. In conclusion, repeated RIPC improves local heating- and SNP-mediated cutaneous VD. When compared with 1 wk of RIPC, 2 wk of RIPC does not induce further improvements in cutaneous VD function.NEW & NOTEWORTHY Repeated RIPC increases the cutaneous vasodilatory response to local heating and to sodium nitroprusside but not to acetylcholine. Thus, endothelial-independent and local heating-mediated cutaneous vasodilation are improved following RIPC. However, 2 wk of RIPC sessions are not more effective than 1 wk of RIPC sessions in enhancing local heating-mediated cutaneous vasodilation.

KCa and KV channels modulate the venoarteriolar reflex in non-glabrous human skin with no roles of KATP channels, NOS, and COX

The venoarteriolar reflex is a local mechanism that induces vasoconstriction during venous congestion in various tissues, including skin. This response is thought to play a critical role in minimizing capillary damage or edema resulting from overperfusion, though factors that modulate this response remain largely unknown. Here, we hypothesized that nitric oxide synthase (NOS), cyclooxygenase (COX), and Ca²⁺-activated, ATP-sensitive, and voltage-gated K⁺ channels (K_Ca, K_ATP, and K_V channels, respectively) modulate the venoarteriolar reflex in human skin. Cutaneous blood flow (laser-Doppler flowmetry) was monitored during a 3-min pre-occlusion baseline and following a 3-min venous occlusion of 45 mmHg, the latter maneuver was used to induce the venoarteriolar reflex. The venoarteriolar reflex was assessed at the following forearm skin sites: Experiment 1 (n = 11): 1) lactated Ringer solution (Control), 2) 10 mM N^ω-nitro-_L-arginine (NOS inhibitor), 3) 10 mM ketorolac (COX inhibitor), and 4) combined NOS + COX inhibition; Experiment 2 (n = 15): 1) lactated Ringer solution (Control), 2) 50 mM tetraethylammonium (K_Ca channel blocker), 3) 5 mM glybenclamide (K_ATP channel blocker), and 4) 10 mM 4-aminopyridine (K_V channel blocker). Separate and combined NOS and COX inhibition as well as K_ATP channel blocker had no effect on venoarteriolar reflex. Conversely, venoarteriolar reflex was attenuated by K_Ca channel blockade (36-38%) and augmented by K_V channel blockade (38-55%). We showed that K_Ca and K_V channels modulate the venoarteriolar reflex with minimum roles of NOS, COX, and K_ATP channels in human non-glabrous forearm skin in vivo. Thus, cutaneous venoarteriolar reflex changes could reflect altered K⁺ channel function.

Historical reviews of the assessment of human cardiovascular function: interrogation and understanding of the control of skin blood flow

Several techniques exist for the determination of skin blood flow that have historically been used in the investigation of thermoregulatory control of skin blood flow, and more recently, in clinical assessments or as an index of global vascular function. Skin blood flow measurement techniques differ in their methodology and their strengths and limitations. To examine the historical development of techniques for assessing skin blood flow by describing the origin, basic principles, and important aspects of each procedure and to provide recommendations for best practise. Venous occlusion plethysmography was one of the earliest techniques to intermittently index a limb’s skin blood flow under conditions in which local muscle blood flow does not change. The introduction of laser Doppler flowmetry provided a method that continuously records an index of skin blood flow (red cell flux) (albeit from a relatively small skin area) that requires normalisation due to high site-to-site variability. The subsequent development of laser Doppler and laser speckle imaging techniques allows the mapping of skin blood flow from larger surface areas and the visualisation of capillary filling from the dermal plexus in two dimensions. The use of iontophoresis or intradermal microdialysis in conjunction with laser Doppler methods allows for the local delivery of pharmacological agents to interrogate the local and neural control of skin blood flow. The recent development of optical coherence tomography promises further advances in assessment of the skin circulation via three-dimensional imaging of the skin microvasculature for quantification of vessel diameter and vessel recruitment.

Severe Hypouricemia Impairs Endothelium-Dependent Vasodilatation and Reduces Blood Pressure in Healthy Young Men: A Randomized, Placebo-Controlled, and Crossover Study

Background

Uric acid (UA) is a plasmatic antioxidant that has possible effects on blood pressure. The effects of UA on endothelial function are unclear. We hypothesize that endothelial function is not impaired unless significant UA depletion is achieved through selective xanthine oxidase inhibition with febuxostat and recombinant uricase (rasburicase).

Methods and Results

Microvascular hyperemia, induced by iontophoresis of acetylcholine and sodium nitroprusside, and heating‐induced local hyperemia after iontophoresis of saline and a specific nitric oxide synthase inhibitor were assessed by laser Doppler imaging. Blood pressure and renin‐angiotensin system markers were measured, and arterial stiffness was assessed. CRP (C‐reactive protein), allantoin, chlorotyrosine/tyrosine ratio, homocitrulline/lysine ratio, myeloperoxidase activity, malondialdehyde, and interleukin‐8 were used to characterize inflammation and oxidative stress. Seventeen young healthy men were enrolled in a randomized, double‐blind, placebo‐controlled, 3‐way crossover study. The 3 compared conditions were placebo, febuxostat alone, and febuxostat together with rasburicase. The allantoin (μmol/L)/UA (μmol/L) ratio differed between sessions (P<0.0001). During the febuxostat‐rasburicase session, heating‐induced hyperemia became altered in the presence of nitric oxide synthase inhibition; and systolic blood pressure, angiotensin II, and myeloperoxidase activity decreased (P≤0.03 versus febuxostat). The aldosterone concentration decreased in the febuxostat‐rasburicase group (P=0.01). Malondialdehyde increased when UA concentration decreased (both P<0.01 for febuxostat and febuxostat‐rasburicase versus placebo). Other parameters remained unchanged.

Conclusions

A large and short‐term decrease in UA in humans alters heat‐induced endothelium‐dependent microvascular vasodilation, slightly reduces systolic blood pressure through renin‐angiotensin system activity reduction, and markedly reduces myeloperoxidase activity when compared with moderate UA reduction. A moderate or severe hypouricemia leads to an increase in lipid peroxidation through loss of antioxidant capacity of plasma.

Clinical Trial Registration

URL: http://www.clinicaltrials.gov. Unique identifier: NCT03395977.

Noninvasive assessment of increases in microvascular endothelial function following repeated bouts of hyperaemia

OBJECTIVE

Spectral analyses of laser-Doppler signal can delineate underlying mechanisms in response to pharmacological agents and in cross-sectional studies of healthy and clinical populations. We tested whether spectral analyses can detect acute changes in endothelial function in response to a 6-week intervention of repeated bouts of hyperaemia.

METHODS

Eleven males performed forearm occlusion (5 s with 10 s rest) for 30 min, 5 times/week for 6 weeks on one arm; the other was an untreated control. Skin blood flow was measured using laser-Doppler fluxmetry (LDF), and endothelial function was assessed with and without nitric oxide (NO) synthase-inhibition with L-NAME in response to local heating (42 °C and 44 °C) and acetylcholine. A wavelet transform was used for spectral analysis of frequency intervals associated with physiological functions.

RESULTS

Basal measures were all unaffected by the hyperaemia intervention (all P > 0.05). In response to local skin heating to 42 °C, the 6 weeks hyperaemia intervention increased LDF, endothelial NO-independent and NO-dependent activity (all P ≤ 0.038). In response to peak local heating (44 °C) endothelial NO-independent and NO-dependent activity increased (both P ≤ 0.01); however, LDF did not (P > 0.2). In response to acetylcholine, LDF, endothelial NO-independent and NO-dependent activity all increased (all P ≤ 0.003) post-intervention.

CONCLUSIONS

Spectral analysis appears sufficiently sensitive to measure changes over time in cutaneous endothelial activity that are consistent with standard physiological (local heating) and pharmacological (acetylcholine) interventions of assessing cutaneous endothelial function, and may be useful not only in research but also clinical diagnosis and treatment.

Impact of the acute local inhibition of soluble epoxide hydrolase on diabetic skin microcirculatory dysfunction

The impact of the local inhibition of soluble epoxide hydrolase, which metabolizes vasodilator and anti-inflammatory epoxyeicosanoids, on diabetic skin microvascular dysfunction was assessed. In diabetic db/db mice, basal skin blood flow assessed using laser Doppler imaging was similar to that of control mice, but thermal hyperemia was markedly reduced. At 2 h after the topical administration of an aqueous gel containing the soluble epoxide hydrolase inhibitor trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid (t-AUCB: 400 mg/L), the peak concentration of t-AUCB was detected in the skin of diabetic mice, which quickly decreased thereafter. In parallel, 2 h after application of t-AUCB treatment, thermal hyperemia was increased compared to the control gel. Quantification of t-AUCB in plasma of treated animals showed no or low systemic diffusion. Furthermore, haematoxylin and eosin histological staining of skin biopsies showed that skin integrity was preserved in t-AUCB-treated mice. Finally, for pig ear skin, a surrogate for human skin, using Franz diffusion cells, we observed a continuous diffusion of t-AUCB from 2 h after application to beyond 24 h. A single topical administration of a soluble epoxide hydrolase inhibitor improves microcirculatory function in the skin of db/db mice and might represent a new therapeutic approach for preventing the development of skin complications in diabetic patients.

Effect of Sex and Menstrual Cycle on Skin Sensory Nerve Contribution to Local Heating

The purpose of this study was to determine sex differences in the contribution of sensory nerves to rapid cutaneous thermal hyperemia. Healthy young females (n = 15, tested during both the early follicular (EF) and the mid-luteal (ML) phase of the menstrual cycle) and males (n = 15) had a 4 cm2 area of skin on one forearm and one leg treated with a eutectic mixture of local anesthetic (EMLA). EMLA sites, along with corresponding control sites, were instrumented with laser Doppler flowmetry probes and local skin heaters. Baseline (33 °C), rapid and sustained vasodilation (42 °C), and maximal vasodilation (44 °C) skin blood flow data were obtained and expressed as a percentage of maximal cutaneous vascular conductance (%CVCmax). Contribution of sensory nerve involvement was determined by comparing the EMLA site to its matched control site utilizing the formula [(% CVCmax control - % CVCmax treatment) / % CVCmax control] × 100. The contribution of sensory nerves to rapid cutaneous thermal hyperemia in the forearm was 24 ± 18 %CVCmax in males, 41 ± 17 %CVCmax in ML females (p = 0.02 vs. males), and 35 ± 17 %CVCmax in EF females (p > 0.05 vs. males). In the leg, the contribution of sensory nerves was 16 ± 15 %CVCmax in males, 34 ± 17 %CVCmax for ML females (p = 0.02 vs. males), and 28 ± 21 %CVCmax in EF females (p > 0.05 vs. males). ML females exhibited a greater contribution of sensory nerves to rapid cutaneous thermal hyperemia in the forearm and leg, possibly attributed to elevated reproductive hormones during the ML phase.

Separate and combined effects of KCa and KATP channel blockade with NOS inhibition on cutaneous vasodilation and sweating in older men during heat stress

Our objective in this study was to examine the separate and combined effects of potassium (K⁺) channels and nitric oxide synthase (NOS) on cutaneous vasodilation and sweating in older men during rest and exercise in the heat. In 13 habitually active men (61 ± 4 yr), cutaneous vascular conductance and local sweat rate were assessed at six dorsal forearm skin sites continuously perfused with either 1) lactated Ringer (control), 2) 10 mM N^G-nitro-l-arginine methyl ester (l-NAME, NOS inhibitor), 3) 50 mM tetraethylammonium (TEA; Ca²⁺-activated K⁺ channel blocker), 4) 5 mM glybenclamide (GLY; ATP-sensitive K⁺ channel blocker), 5) 50 mM TEA + 10 mM l-NAME, and 6) 5 mM GLY + 10 mM l-NAME via microdialysis. Participants rested in non-heat stress (25°C) and heat stress (35°C) conditions for ∼60 min each, followed by 50 min of moderate-intensity cycling (∼55% V̇o_2peak) and 30 min of recovery in the heat. During rest and exercise in the heat, l-NAME, TEA + l-NAME, and GLY + l-NAME attenuated CVC relative to control (all P ≤ 0.05), although l-NAME was not different from TEA + l-NAME or GLY + l-NAME (all P > 0.05). TEA attenuated CVC during rest, whereas GLY attenuated CVC during exercise (both P ≤ 0.05). Additionally, whereas neither l-NAME nor TEA altered sweating throughout the protocol (all P > 0.05), combined TEA + l-NAME attenuated sweating during exercise in the heat (P ≤ 0.05). We conclude that in habitually active older men blockade of K_Ca and K_ATP channels attenuates cutaneous vasodilation during rest and exercise in the heat, respectively, and these effects are NOS dependent. Furthermore, combined NOS inhibition and K_Ca channel blockade attenuates sweating during exercise in the heat.

Sunscreen or simulated sweat minimizes the impact of acute ultraviolet radiation on cutaneous microvascular function in healthy humans

NEW FINDINGS

What is the central question of this study? Are ultraviolet radiation (UVR)-induced increases in skin blood flow independent of skin erythema? Does broad-spectrum UVR exposure attenuate NO-mediated cutaneous vasodilatation, and does sunscreen or sweat modulate this response? What are the main findings and their importance? Erythema and vascular responses to UVR are temporally distinct, and sunscreen prevents both responses. Exposure to UVR attenuates NO-mediated vasodilatation in the cutaneous microvasculature; sunscreen or simulated sweat on the skin attenuates this response. Sun over-exposure may elicit deleterious effects on human skin that are separate from sunburn, and sunscreen or sweat on the skin may provide protection.

ABSTRACT

Exposure to ultraviolet radiation (UVR) may result in cutaneous vascular dysfunction independent of erythema (skin reddening). Two studies were designed to differentiate changes in erythema from skin vasodilatation throughout the 8 h after acute broad-spectrum UVR exposure with (+SS) or without SPF-50 sunscreen (study 1) and to examine NO-mediated cutaneous vasodilatation after acute broad-spectrum UVR exposure with or without +SS or simulated sweat (+SW) on the skin (study 2). In both studies, laser-Doppler flowmetry was used to measure red cell flux, and cutaneous vascular conductance (CVC) was calculated (CVC = flux/mean arterial pressure). In study 1, in 14 healthy adults (24 ± 4 years old; seven men and seven women), the skin erythema index and CVC were measured over two forearm sites (UVR only and UVR+SS) before, immediately after and every 2 h for 8 h post-exposure (750 mJ cm^-2 ). The erythema index began to increase immediately post-UVR (P < 0.05 at 4, 6 and 8 h), but CVC did not increase above baseline for the first 4-6 h (P ≤ 0.01 at 6 and 8 h); +SS prevented both responses. In study 2, in 13 healthy adults (24 ± 4 years old; six men and seven women), three intradermal microdialysis fibres were placed in the ventral skin of the forearm [randomly assigned to UVR (450 mJ cm^-2 ), UVR+SS or UVR+SW], and one fibre (non-exposed control; CON) was placed in the contralateral forearm. After UVR, a standardized local heating (42°C) protocol quantified the percentage of NO-mediated vasodilatation (%NO). The UVR attenuated %NO compared with CON (P = 0.01). The diminished %NO was prevented by +SS (P < 0.01) and +SW (P < 0.01). Acute broad-spectrum UVR attenuates NO-dependent dilatation in the cutaneous microvasculature, independent of erythema. Sunscreen protects against both inflammatory and heating-induced endothelial dysfunction, and sweat might prevent UVR-induced reductions in NO-dependent dilatation.

Effects of aerobic exercise on vascular function in nondialysis chronic kidney disease: a randomized controlled trial

Endothelial dysfunction and arterial stiffness are nontraditional risk factors of chronic kidney disease (CKD)-related cardiovascular disease (CVD) that could be targeted with exercise. This study investigated the effect of moderate to vigorous aerobic exercise on vascular function in nondialysis CKD. In this randomized, controlled trial, 36 nondialysis patients with CKD (means ± SE, age: 58 ± 2 yr, estimated glomerular filtration rate: 44 ± 2 ml·min-1·1.73 m-2) were allocated to an exercise training (EXT) or control (CON) arm. The EXT group performed 3 × 45 min of supervised exercise per week at 60-85% heart rate reserve for 12 wk, whereas the CON group received routine care. Outcomes were assessed at 0 and 12 wk. The primary outcome, microvascular function, was assessed via cutaneous vasodilation during local heating measured by laser-Doppler flowmetry coupled with microdialysis. Participants were instrumented with two microdialysis fibers for the delivery of 1) Ringer solution and 2) the superoxide scavenger tempol. Conduit artery function was assessed via brachial artery flow-mediated dilation. Aortic pressure waveforms and pulse wave velocity were acquired with tonometry and oscillometry. Microvascular function improved after EXT (week 0 vs.week 12, EXT: 87 ± 2% vs. 91 ± 2% and CON: 86 ± 2% vs. 84 ± 3%, P = 0.03). At baseline, pharmacological delivery of tempol improved microvascular function (Ringer solution vs. tempol: 86 ± 1% vs. 90 ± 1%, P = 0.02) but was no longer effective after EXT (91 ± 2% vs. 87 ± 1%, P = 0.2), suggesting that an improved redox balance plays a role in EXT-related improvements. Brachial artery flow-mediated dilation was maintained after EXT (EXT: 2.6 ± 0.4% vs. 3.8 ± 0.8% and CON: 3.5 ± 0.6% vs. 2.3 ± 0.4%, P = 0.02). Central arterial hemodynamics and arterial stiffness were unchanged after EXT. Aerobic exercise improved microvascular function and maintained conduit artery function and should be considered as an adjunct therapy to reduce CVD risk in CKD.

The reliability of cutaneous low-frequency oscillations in young healthy males

OBJECTIVE

Spectral analyses of laser-Doppler flowmetry measures enable a simple and non-invasive method to investigate mechanisms regulating skin blood flow. We assessed within-day and day-to-day variability of cutaneous spectral analyses.

METHODS

Eleven young, healthy males were tested twice in three identical sessions, with 19 to 24 days between visits, for a total of six tests. Wavelet data were analyzed at rest, in response to local skin heating to 42 and 44°C, and during 5-minutes PORH. We did this for six frequency bands commonly associated with physiological functions. To assess reliability, we calculated CV and ICC scores.

RESULTS

At rest, mean CV for the wavelet data ranged from 21% to 24% and ICC scores ranged from 0.67 to 0.91. During local heating, mean CV scores ranged from 17% to 22% and mean ICC scores ranged from 0.71 to 0.95. For peak PORH, CV ranged from 14% to 23% and the ICC range was 0.88 to 0.97. For the area under the curve of the PORH, CV range was 12% to 21% and ICC range was 0.81 to 0.92.

CONCLUSIONS

These analyses indicate good-to-excellent reliability of the wavelet data in healthy young males.

Seven consecutive days of remote ischaemic preconditioning improves cutaneous vasodilatory capacity in young adults

KEY POINTS

Remote ischaemic preconditioning (RIPC), induced by brief bouts of ischaemia followed by reperfusion, confers vascular adaptations that protect against subsequent bouts of ischaemia; however, the effect of RIPC repeated over several days on the human microcirculation is unknown. Using skin as a model, microvascular function was assessed at a control and a NO-inhibited area of skin before 1 day after and 1 week after administering seven consecutive days of repeated RIPC on the contralateral arm. Maximal vasodilatation was increased by ∼20-50% following 7 days of repeated RIPC, and this response remained elevated 1 week after stopping RIPC; however, NO-mediated vasodilatation was not affected by the RIPC stimulus. These data indicate that repeated RIPC augments maximal vasodilatation, but the underlying mechanism for this improvement is largely independent of NO. This finding suggests a role for other endothelium-derived mediators and/or for endothelium-independent adaptations with repeated RIPC.

ABSTRACT

Remote ischaemic preconditioning (RIPC), induced by intermittent periods of ischaemia followed by reperfusion, confers cardiovascular protection from subsequent ischaemic bouts. RIPC increases conduit and resistance vessel function; however, the effect of RIPC on the microvasculature remains unclear. Using human skin as a microvascular model, we hypothesized that cutaneous vasodilatory (VD) function elicited by localized heating would be increased following repeated RIPC. Ten participants (23 ± 1 years, 6 males, 4 females) performed RIPC for seven consecutive days. Each daily RIPC session consisted of 4 repetitions of 5 min of arm blood flow occlusion interspersed by 5 min reperfusion. Before, 1 day after and 1 week after the 7 days of RIPC, two microdialysis fibres were placed in ventral forearm skin for continuous infusion of Ringer solution or 20 mM l-NAME. Red blood cell flux was measured by laser Doppler flowmetry at each fibre site during local heating (T_loc  = 39°C) and during maximal VD elicited by heating (T_loc  = 43°C) and 28 mM sodium nitroprusside infusion. Data were normalized to cutaneous vascular conductance (flux/mmHg). Seven days of RIPC did not alter the nitric oxide (NO) contribution to the VD response to local heating (P > 0.05). However, the maximal VD was augmented (Pre: 2.5 ± 0.2, Post: 3.8 ± 0.5 flux/mmHg; P < 0.05) and remained elevated 1 week post RIPC (3.3 ± 0.4 flux/mmHg; P < 0.05). Repeated RIPC improves maximal VD but does not affect NO-mediated VD in the cutaneous microvasculature. This finding suggests that other factors may explain the vasodilatory adaptations that occur following repeated RIPC.

Cutaneous vasomotor responses in boys and men

Few studies have investigated skin blood flow in children and age-related differences in the underlying mechanisms. We examined mechanisms of skin blood flow responses to local heating, postocclusive reactive hyperaemia (PORH), and isometric handgrip exercise in adult and prepubescent males, hypothesizing that skin blood flow responses would be greater in children compared with adults. We measured skin blood flow in 12 boys (age, 9 ± 1 years) and 12 men (age, 21 ± 1 years) using laser-Doppler flowmetry at rest, in response to 3-min PORH, 2-min isometric handgrip exercise, and local skin heating to 39 °C (submaximal) and 44 °C (maximal). Using wavelet analysis we assessed endothelial, neural, and myogenic activities. At rest and in response to local heating to 39 °C, children had higher skin blood flow and endothelial activity compared with men (d ≥ 1.1, p < 0.001) and similar neurogenic and myogenic activities (d < 0.2, p > 0.05). Maximal responses to 44 °C local skin heating, PORH, and isometric handgrip exercise did not differ between boys and men (all d ≤ 0.2, p > 0.05). During PORH children demonstrated greater endothelial activity compared with men (d ≥ 0.6, p < 0.05); in contrast, men had higher neurogenic activity (d = 1.0, p < 0.01). During isometric handgrip exercise there were no differences in endothelial, neurogenic, and myogenic activities (d < 0.2, p > 0.3), with boys and men demonstrating similar increases in endothelial activity and decreases in myogenic activity (d ≥ 0.8, p < 0.05). These data suggest that boys experience greater levels of skin blood flow at rest and in response to submaximal local heating compared with men, while maximal responses appear to be similar. Additionally, endothelial mediators seem to contribute more to vasodilatation in boys than in men.

Acute ultraviolet radiation exposure attenuates nitric oxide-mediated vasodilation in the cutaneous microvasculature of healthy humans

5-methyltetrahydrofolate (5-MTHF) is important for nitric oxide (NO)-mediated cutaneous microvascular vasodilation. Ultraviolet B (UVB) radiation may deplete 5-MTHF, either directly or via production of reactive oxygen species (ROS), decreasing NO-mediated vasodilation. We hypothesized that 1) acute UVB exposure would attenuate NO-dependent cutaneous vasodilation, 2) local perfusion of 5-MTHF or ascorbate (ASC; anti-oxidant) would augment NO-dependent vasodilation after UVB, and 3) darker skin pigmentation would be UVB-protective. Three intradermal microdialysis fibers placed in each forearm of 21 healthy young adults (23±1 yr; 8M/13F) locally delivered lactated Ringer's (control), 5mM 5-MTHF, or 10mM ASC. One arm was UVB-exposed (300mJ/cm²), the other served as non-exposed control (CON). Following UVB exposure, a standardized local heating (42˚C) protocol induced cutaneous vasodilation. After attaining a plateau blood flow, 15mM N^G-nitro-L-arginine methyl ester (L-NAME; nitric oxide synthase inhibiter) was infused at all sites to quantify the NO contribution. Red cell flux was measured at each site by laser-Doppler flowmetry (LDF) and cutaneous vascular conductance (CVC=LDF/MAP) was expressed as a percentage of maximum (%CVC_max; 28mM sodium nitroprusside+43°C). UVB attenuated NO-mediated vasodilation compared to CON (23.1±3.6 vs 33.9±3.4 %; p=0.001). Delivery of 5-MTHF or ASC improved NO-mediated vasodilation versus lactated Ringer's in the UVB-exposed arm (MTHF: 30.1±4.8 vs 23.1±3.8 %; p=0.03; ASC: 30.9±4.3 vs 23.1±3.8 %; p=0.02). Neither treatment affected the response in the non-exposed arm (p≥0.09). Skin pigmentation (M-index) was not predictive of the UVB response (p≥0.34). These data suggest that acute UVB exposure attenuates NO-mediated vasodilation via direct and/or ROS-induced reductions in 5-MTHF, independent of skin pigmentation.

Sex differences in the mechanisms mediating blunted cutaneous microvascular function in young black men and women

The black population exhibits attenuated vasodilatory function across their lifespan, yet little is known regarding the mechanisms of this impairment. Recent evidence suggests a potential role for oxidative stress. Therefore, we tested the hypothesis that NADPH oxidase (NOX) and/or xanthine oxidase (XO) contribute to blunted nitric oxide (NO)-mediated cutaneous microvascular function in young black adults. In 30 white and black subjects (8 men and 7 women in each group), local heating was performed while NOX and XO were inhibited by apocynin and allopurinol, respectively, via intradermal microdialysis. The plateau in cutaneous vascular conductance (red blood cell flux/mean arterial pressure) during 39°C local heating at each site was compared with a control site perfused with lactated Ringer solution. Subsequent inhibition of NO synthase via N^ω-nitro-l-arginine methyl ester allowed for quantification of the NO contribution to vasodilation during heating. Black individuals, relative to white individuals, had a blunted cutaneous vascular conductance plateau at the control site (45 ± 9 vs. 68 ± 13%max, P < 0.001) that was increased by both apocynin (61 ± 15%max, P < 0.001) and allopurinol (58 ± 17%max, P = 0.005). Black men and black women had similar responses to heating at the control site ( P = 0.99), yet apocynin and allopurinol increased this response only in black men (both P < 0.001 vs. control). The NO contribution was also increased via apocynin and allopurinol exclusively in black men. These findings suggest that cutaneous microvascular function is reduced because of NOX and XO activity in black men but not black women, identifying a novel sex difference in the mechanisms that contribute to blunted vascular responses in the black population. NEW & NOTEWORTHY We demonstrate that cutaneous microvascular responses to local heating are consistently reduced in otherwise healthy young black men and women relative to their white counterparts. Inhibition of NADPH oxidase and xanthine oxidase via apocynin and allopurinol, respectively, augments microvascular function in black men but not black women. These data reveal clear sex differences in the mechanisms underlying the racial disparity in cutaneous microvascular function.

Blood pressure normalization via pharmacotherapy improves cutaneous microvascular function through NO-dependent and NO-independent mechanisms

Hypertension is associated with endothelial dysfunction and vascular remodeling.

OBJECTIVE

To assess effects of antihypertensive pharmacotherapy on eNOS- and iNOS-dependent mechanisms and maximal vasodilator capacity in the cutaneous microvasculature.

METHODS

Intradermal microdialysis fibers were placed in 15 normotensive (SBP 111±2 mm Hg), 12 unmedicated hypertensive (SBP 142±2 mm Hg), and 12 medicated hypertensive (SBP 120±2 mm Hg) subjects. Treatments were control, iNOS-inhibited (1400w), and NOS-inhibited (l-NAME). Red cell flux, measured during local heating (42°C) and ACh dose-response protocols, was normalized to CVC (flux MAP^-1 ) and a percentage of maximal vasodilation (%CVC_max ).

RESULTS

Compared to normotensives, ACh-mediated vasodilation was attenuated in the hypertensive (P<.001), but not in medicated subjects (P=.83). NOS inhibition attenuated ACh-mediated vasodilation in normotensives compared to hypertensive (P<.001) and medicated (P<.001) subjects. With iNOS inhibition, there was no difference in ACh-mediated vasodilation between groups. Compared to the normotensives, local heat-induced vasodilation was attenuated in the hypertensives (P<.001), but iNOS inhibition augmented vasodilation in the hypertensives so this attenuation was abolished (P=.31). Compared to normotensives, maximal vasodilator capacity was reduced in the hypertensive (P=.014) and medicated subjects (P=.004).

CONCLUSIONS

In the cutaneous microvasculature, antihypertensive pharmacotherapy improved endothelial function through NO-dependent and NO-independent mechanisms, but did not improve maximal vasodilator capacity.

Attenuated cutaneous microvascular function in healthy young African Americans: Role of intradermal l-arginine supplementation

It has been established that endothelial function in conduit vessels is reduced in young African Americans (AA) relative to Caucasian Americans (CA). However, less is known regarding endothelial function in microvasculature of young AA. We hypothesized that microvascular function in response to local heating of skin is attenuated in young AA relative to age-matched CA due largely to the lack of NO bioavailability, which is in turn improved by intradermal l-arginine supplementation and/or inhibition of arginase. Nine AA and nine CA adults participated in this study. Participants were instrumented with four microdialysis membranes in the cutaneous vasculature of one forearm and were randomly assigned to receive 1) lactated Ringer's solution as a control site; 2) 20 mM NG-nitro-l-arginine (l-NAME) to inhibit NO synthase activity; 3) 10 mM l-arginine to local supplement l-arginine; or 4) a combination of 5.0 mM (S)-(2‑boronoethyl)-l-cysteine-HCL (BEC) and 5.0 mM Nω-hydroxy-nor-l-arginine (nor-NOHA) at a rate of 2.0 μl/min to locally inhibit arginase activity. Cutaneous vascular conductance (CVC) was calculated as red blood cell flux divided by mean arterial pressure. All CVC data were presented as a percentage of maximal CVC (%CVCmax) that was determined by maximal cutaneous vasodilation induced by 44 °C heating plus sodium nitroprusside administration. The response during the 42 °C local heating plateau was blunted in the AA at the control site (CA: 84 ± 12 vs. AA: 62 ± 6 vs. %CVCmax; P < 0.001). This response was improved in AA at the l-arginine site (Control: 62 ± 6 vs. l-arginine: 70 ± 18%CVCmax; P < 0.05) but not in the arginase inhibited site (Control: 62 ± 6 vs. Arginase inhibited: 62 ± 13%CVCmax; P = 0.91). In addition, the AA group had an attenuated NO contribution to the plateau phase during 42 °C local heating relative to the CA group (CA: 56 ± 14 vs. AA: 44 ± 6 Δ %CVCmax; P < 0.001). These findings suggest that 1) cutaneous microvascular function in response to local heating is blunted in young AA when compared to age-matched young CA; 2) this attenuated response is partly related to decrease in NO bioavailability in young AA; and 3) a local infusion of l-arginine, but not arginase inhibition, improves cutaneous microvascular responses to local heating in young AA relative to CA.

Acute vascular effects of carbonated warm water lower leg immersion in healthy young adults

Endothelial dysfunction is associated with increased cardiovascular mortality and morbidity; however, this dysfunction may be ameliorated by several therapies. For example, it has been reported that heat‐induced increases in blood flow and shear stress enhance endothelium‐mediated vasodilator function. Under these backgrounds, we expect that carbon dioxide (CO₂)‐rich water‐induced increase in skin blood flow improves endothelium‐mediated vasodilation with less heat stress. To test our hypothesis, we measured flow‐mediated dilation (FMD) before and after acute immersion of the lower legs and feet in mild warm (38°C) normal or CO₂‐rich tap water (1000 ppm) for 20 min in 12 subjects. Acute immersion of the lower legs and feet in mild warm CO₂‐rich water increased FMD (P < 0.01) despite the lack of change in this parameter upon mild warm normal water immersion. In addition, FMD was positively correlated with change in skin blood flow regardless of conditions (P < 0.01), indicating that an increase in skin blood flow improves endothelial‐mediated vasodilator function. Importantly, the temperature of normal tap water must reach approximately 43°C to achieve the same skin blood flow level as that obtained during mild warm CO₂‐rich water immersion (38°C). These findings suggest that CO₂‐rich water‐induced large increases in skin blood flow may improve endothelial‐mediated vasodilator function while causing less heat stress.

Flow motion dynamics of microvascular blood flow and oxygenation: Evidence of adaptive changes in obesity and type 2 diabetes mellitus/insulin resistance

An altered spatial heterogeneity and temporal stability of network perfusion can give rise to a limited adaptive ability to meet metabolic demands. Derangement of local flow motion activity is associated with reduced microvascular blood flow and tissue oxygenation, and it has been suggested that changes in flow motion activity may provide an early indicator of declining, endothelial, neurogenic, and myogenic regulatory mechanisms and signal the onset and progression of microvascular pathophysiology. This short conference review article explores some of the evidence for altered flow motion dynamics of blood flux signals acquired using laser Doppler fluximetry in the skin in individuals at risk of developing or with cardiometabolic disease.